Table of Contents Basics of EIGRP Basics of EIGRP Configuration EIGRP Configuration Monitoring EIGRP Monitoring EIGRP Chapter 6 Lab Notes Chapter 6 Lab

Table of ContentsTable of Contents

Basics of EIGRPBasics of EIGRP

EIGRP ConfigurationEIGRP Configuration

Monitoring EIGRPMonitoring EIGRP

Chapter 6 Lab NotesChapter 6 Lab Notes

EIGRP TerminologyEIGRP Terminology

EIGRP OperationEIGRP Operation

Basics of EIGRPBasics of EIGRP


End Slide ShowEnd Slide Show

EIGRP OverviewEIGRP OverviewEnhanced version of Cisco’s proprietary IGRP dramatically increases operational efficiency because EIGRP…• Uses a more granular version of IGRP’s metrics (32 bits v.

24 bits)• Has faster convergence than any other IGP• Is scalable because of VLSM and route summarization• Supports multiple routed protocols through protocol-

dependant modules• Replaces Novell RIP and Apple’s RTMP• Is technically an advance distance-vector routing protocol

Uses partial updates Hello packets for neighbor discovery

• Is relatively easy to administer However, does not have OSPF’s hierarchical design (no areas)

EIGRP MetricsEIGRP MetricsEIGRP scales IGRP’s metrics by a factor of 256• IGRP metric = 24 bits; EIGRP metric = 32 bits• Bandwidth and Delay are equally weighted• Reliability, Load, and MTU are off by default• Hop count limited to 224 (IGRP’s limit is 255)

To remember the metric components…• Big = Bandwidth• Dogs = Delay• Really = Reliability• Like = Load• Me = MTU

EIGRP TablesEIGRP TablesLike OSPF, EIGRP maintains three unique tables to assist in routing traffic.• Neighbor Table• Topology Table• Routing Table

EIGRP maintains one table of each for each routed protocol configured on the router. • For example, if a router was configured with IP,

IPX and AppleTalk, EIGRP would maintain…3 Neighbor Tables3 Topology Tables3 Routing Tables

Neighbor TableNeighbor TableUse the show ip eigrp neighbors command to view the table.• Similar to OSPF’s Adjacencies database;

Contains a list of all neighbors discovered through hellosMaintains hello and holdtime intervals on each neighborMaintains information required by RTP (discussed later)SRTT—Smooth Round-trip Timer; avg. time it takes to

send and then receive a reply from that neighborRTO—Retransmission Timeout; how long to wait without

receiving an acknowledgement to a reliably sent packet

Router#show ip eigrp neighbors

IP-EIGRP neighbors for process 100H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num0 192.168.224.2 Se0 13 00:01:28 930 5000 0 301 192.168.208.2 Se1 11 00:02:20 35 1140 0 21

Topology TableTopology TableUse the show ip eigrp topology [all-links] command to view the table.• Similar to OSPF’s Link-State (Topology) database;

Contains all routes the router has learned about from its neighbors and all the information necessary to calculate a set of distances and vectors to all reachable destinations

FD—Feasible Distance; lowest calculated metric to reach a destination as opposed to…

RD—Reported Distance or Advertised Distance; distance to the destination reported by the neighbor.

Router#show ip eigrp topology

IP-EIGRP Topology Table for process 100Codes: P – Passive, A – Active, U – Update, Q – Query, R – Reply, r – Reply status

P 192.150.42.120 255.255.255.248, 1 successors, FD is 2172416

via 192.150.42.9 (2172416/2169856), Fddi0

P 192.150.42.8 255.255.255.248, 1 successors, FD is 28160

via Connected, Fddi0

Feasible Distance Reported

Distance

Routing TableRouting TableUse the show ip route command to view tableLike all routing protocols, EIGRP maintains a routing table with…• Best routes to destination networks• Maintains up to four equal-cost routes for each

destinationUnequal-cost routes can be installed if the variance

command has been configured

• You are already familiar with the routing table. You will notice that EIGRP routes are designated with a D.

EIGRP TerminologyEIGRP Terminology



EIGRP Concepts & TerminologyEIGRP Concepts & TerminologySuccessor• The best, least cost route to the destination installed in the

routing table; multiple successors can be installed for load balancing

Feasible Successor• A next-hop alternative route to the destination kept in the

topology table, ready to be installed if the successor fails; feasible successors are only in the topology table

Active State• During route recomputation, routes lost due to a

successor’s failure are said to be in the active state. The active state ends when the route is restored or removed.

Passive State• Installed routes that are not in the process of being

recomputed are said to be in the passive state.

EIGRP Concepts & TerminologyEIGRP Concepts & TerminologyDiffusing Update Algorithm (DUAL)• EIGRP’s route computation engine; guarantees a loop-free

topology; calculates EIGRP’s metric and installs successors in the routing table & feasible successors in the topology table

Route Evaluation• Occurs when the topology changes; DUAL evaluates the

topology table, searching for feasible successors and immediately installing them, if found; no recomputation is necessary

Route Recomputation• DUAL begins recomputing if no feasible successors are

found; queries neighbors for alternative routes; process ends when all neighbors have replied and DUAL either installs successor or removes route from the topology and routing tables.

Protocol Dependant Modules (PDM)• EIGRP’s scalable and adaptable feature because of its

modularity; theoretically, EIGRP does not have to be completely rewritten to route IPv6—just add a PDM.

EIGRP Packet TypesEIGRP Packet TypesHello Packets• Unreliable multicast to 224.0.0.10 to discover and

maintain neighbors; contains the router’s neighbor table• Default hello interval depends on the bandwidth

≤ 1.544 Mbps = 60 sec. hello interval (180 holdtime)> 1.544 Mbps = 5 sec. hello interval (15 holdtime)

Update Packets• Sent reliably, there are 2 types

Unicast to new neighbor discover; contains routing table Multicast to all neighbors when topology changes

Query & Reply Packets• Queries are multicast reliably during route recomputation,

querying neighbors for a new successor to a lost route• Neighbors unicast a reply to the query whether or not they

have a route.Acknowledgement Packets• “Dataless” packet that acknowledges the receipt of a

packet sent reliably

Reliable Transport ProtocolReliable Transport ProtocolRTP is EIGRP’s flexible protocol used to transport message types through a network• Since EIGRP is protocol independent, it has to

have its own connection-oriented and connectionless services

• RTP allows unicasting and multicasting reliable and unreliable packets to peers simultaneously

• RTP maintains a transmission list in the neighbor table with sequence numbers to determine when a required acknowledgement has been received.Works much like TCP’s Positive Acknowledgement with

Retransmission

EIGRP OperationEIGRP Operation



EIGRP operation is completed in five stages:• Building neighbor relationships• Discovering routes• Choosing the best routes• Maintaining routes• Removing routes

These stages do not necessarily occur sequentially• Building relationships and discovering routes occur

together as do choosing and maintaining routers

Note: The following EIGRP Operation discussion is adapted from CCNP Routing Exam Prep: Exam 640-503 (© 2000) by Robert Larson, et al.

The EIGRP ProcessThe EIGRP Process

Building Neighbor RelationshipsBuilding Neighbor RelationshipsNeighbor relationships are established through the use of Hello packets• A new router configured with EIGRP will multicast

hello packets to directly connected routers• The receiving routers will reply if the new router

is…Configured with EIGRPIn same ASUsing the same metric weights

• EIGRP routers, unlike OSPF, do not have to have the same hello intervalsDefaults, however, are 5 sec. for > T1 and 60 sec. for ≤

T1.

Discovering RoutesDiscovering RoutesWhile neighbor relationships are established, the following steps occur:• The new router multicast hellos to 224.0.0.10• Directly connected routers respond with a

unicast update packet containing all the routes in their routing table

• The new router replies to all neighbors with a unicast Ack packet and places the contents of the updates in its topology table

• The new router then unicast update packets to all neighbors with the contents of its topology table (this is how its neighbors learn about the router’s uniquely configured networks such as a new LAN)

• Neighbors reply to the new router’s update with an Ack packet.

Building/Discovering ExampleBuilding/Discovering Example

1. C comes online and multicasts hellos to A & B.

2. A & B unicast an update packet containing routing table contents

3. C replies to unicast updates with Ack packet and builds topology table

4. C unicasts updates to A & B with contents of topology table (includes C’s new LAN)

5. A & B reply with an Ack packet.

A B

C

Choosing the Best RoutesChoosing the Best RoutesAfter a new router has received all the updates from directly connected neighbors, it can calculate its DUAL.• First, the metric for each route in the topology

table is calculated using the following formula:Metric = 256[(10,000,000/min. bandwidth) + sum of delays]

• Then, the route with the lowest cost is designated the successor and is installed (up to 4 with equal costs) in the routing table.

• DUAL then looks for feasible successors. A feasible successor must have a lower feasible distance to the destination than the installed route’s feasible distance.

• All feasible successors are maintained in the topology table so DUAL can install them immediately if the successor fails.

Maintaining RoutesMaintaining RoutesAs new routers come online and old routes fail, EIGRP quickly and efficiently handles these situations with little or no downtime.• As new routers come online, their hello packets

and the ensuing update process has a “domino effect” on the network.

• All routers in the AS almost instantaneously converge on the router’s new networks.

Maintaining routes also means informing directly connected neighbors when another neighbor stops sending hello packets at the required interval.

Removing RoutesRemoving RoutesWhen a route fails (a directly connected neighbor is no longer sending hellos), the detecting router’s DUAL…• Enters the route evaluation phase.

Is there a feasible successor in the topology table? If so, immediately install it, begin routing to the alternative path, and update neighbors about the alternative.

If no feasible successor exists, enter route recomputation

• If necessary, enter the route recomputation phase. Query neighbors for a alternative route

– If neighbor has a feasible successor, it will send it to the router– If it does not have one, it will query all its directly connected

neighbors, thus flooding the AS with the query until an alternate route is or is not found.

Once the router has received replies from all queried neighbors, it can then recalculate the best route.

– If a new alternative is found, it will be installed in the routing table.– If no new alternative is found, the old route is removed.

EIGRP Convergence SummaryEIGRP Convergence Summary1. Router detects link failure; enters route evaluation

Feasible successors are promoted to successors Successors are installed in the routing table immediately All neighbors are updated about the new alternate route

2. If no feasible successors, router enters route recomputation Queries are flooded throughout the AS in search of an alternate All routers reply whether they have an alternative or not Originating router waits for all replies before either

– Removing the queried network for its topology and routing tables or– Adding an alternative path for the queried network in its tables

If a query receives no response, the route becomes “stuck-in-active”

3. The router has now converged and will now work to converge the entire internetwork by… Generating an update and multicasting it out all interfaces

– Update contains info. on what paths the router has added/removed from its topology and routing tables

Each receiving router will replay with an Ack packet and modify tables accordingly– The EIGRP internetwork has now converged.

EIGRP ConfigurationEIGRP Configuration



Similar to IGRP, EIGRP is started with the following commands:Router(config)#router eigrp [AS_number]Router(config-router)#network network-number• A router running both IGRP and EIGRP with the same AS

number will automatically redistribute from one routing process into the other EIGRP routes redistributed into IGRP are denoted with an “I”

in the routing table. IGRP routes redistributed into EIGRP are denoted with an “D

EX” in the routing table.

For interfaces whose actual bandwidth is different than EIGRP’s defaults, use the following command.Router(config-if)#bandwidth kilobits• For example, a serial link defaults to T1 speeds or 1544

kbps. If the contracted speed is ½ a T1 or 768 kbps…Router(config-if)#bandwidth 768

Basic ConfigurationBasic Configuration

Route SummarizationRoute SummarizationEIGRP recognizes two types of summary routing:• Automatic route summarization• Manual route summarization

Automatic Summarization (on by default in EIGRP)• Works the same as IGRP and RIP

Summarizes routes on the classful boundary; does not advertise subnets; subnets must be contiguous.

For example;– Subnets 172.16.16.0/20, 172.16.32.0/20, and 172.16.48.0/20

would be automatically summarized as 172.16.0.0/16 Automatic summarization has its benefits

– Conserves resources across classful boundaries in networks with proper IP addressing design.

Manual Summarization• EIGRP can summarize routes at classless boundaries on

any router interface on the network This capability is an advantage over OSPF, which can only

summarize on ABRs and ASBRs

Manual SummarizationManual SummarizationAutomatic summarization must be turned off.• in the routing process for EIGRP…Router(config-router)#no auto-summary

To configure a classless summary route…• Subnets must be contiguous!!• Use the following command on the interface that

will advertise the summary:Router(config-if)#ip summary-address eigrp AS-number ip-address mask

Manual Summarization Manual Summarization ExampleExample

On Router B, you would summarize routes advertised to A as follows:!Start the routing process & disable automatic summarization

RTB(config)#router eigrp 100

RTB(config-router)#network 190.1.1.0



RTB(config-router)#no auto-summary

!Then on the interface, summarize the subnets advertised to A

RTB(config-router)#interface e0

RTB(config-if)#ip address 10.2.50.1 255.255.255.0

RTB(config-if)#ip summary-address eigrp 100 190.1.0.0 255.255.252.0

BA C

D

e0e1

e2

190.1.1.0/24

190.1.3.0/24

190.1.2.0/24

10.2.10.0/24

10.2.50.0/24

190.1.0.0/22Advertised to A

Null0 means there’s no specific interface

for 190.1.1.0/22; more specific routes exist.


Router B’s topology table would show all the specific routes as well as the summary:RTB#show ip eigrp topologyIP-EIGRP Topology Table for process 1

(output omitted)

P 190.1.1.0/24, 1 successors, FD is 10511872via Connected, Serial1

P 190.1.0.0/22, 1 successors, FD is 10511872via Summary (10511872/0), Null0

P 190.1.3.0/24, 1 successors, FD is 10639872via 190.1.1.1 (10639872/128256), Serial1

P 190.1.2.0/24, 1 successors, FD is 10537472via 190.1.1.1 (10639872/128256), Serail1

BA C

D

e0e1

s1

190.1.1.0/24

190.1.3.0/24

190.1.2.0/24

10.2.10.0/24

10.2.50.0/24


Router A’s topology table would show only the summary route:• Any packet destined for a network that is part of

the 190.1.0.0/22 summary would be sent to Router B.

RTA#show ip eigrp topologyIP-EIGRP Topology Table for process 1

(output omitted)

P 190.1.0.0/22, 1 successors, FD is 11023872via 10.2.50.1 (11023872/10511872), Serial0


BA C

D

e0e1

s1

190.1.1.0/24

190.1.3.0/24

190.1.2.0/24

10.2.10.0/24

10.2.50.0/24


Bandwidth OptimizationBandwidth OptimizationBy default, EIGRP will only consume up to 50% of a link’s configured bandwidth.• If a link in 256Kbps, then EIGRP traffic will use up to

128Kbps

Why would you want to change the default setting?• May be necessary when network apps require certain

amounts of bandwidth at all times.• Sometimes, EIGRP traffic will require a certain level of

bandwidth availability.

Note: Changing EIGRP’s bandwidth percentage has no effect on user traffic.Two commands to configure EIGRP traffic percentage.• bandwidth• ip bandwidth-percent eigrp

bandwidthbandwidth Configuration ConfigurationThe bandwidth commandRouter(config-if)#bandwidth bandwidth• Configured on the interface where you want to

adjust EIGRP traffic.• Whatever value is specified with the bandwidth

command, EIGRP always takes 50% of it (by default).

• Remember: The bandwidth command is only used by routing protocols—it has no effect on user traffic when the protocol is EIGRP. The router does not use this command for any other purpose.

• For example, you have a 128kbps link and you only want EIGRP to use 16kbps.

Router(config-if)bandwidth 32EIGRP will use, at most, 50% of the configured bandwidthUser traffic will still be allowed to use at least 112kbps

(128-16)

AS #

The second way to modify how much bandwidth EIGRP uses is to use the following command:Router(config-if)#ip bandwidth-percent eigrp AS-number percent

Use this command when you want to specify a different percentage than 50% of the configured bandwidth.• For example, you have a 64kbps link and the

bandwidth has been set to 32kbps for metric calculation purposes.

• However, you want EIGRP to be able to use an entire 32kbps of the link’s 64kbps speed, if needed.

Router(config)#int s0

Router(config-if)#bandwidth 32

Router(config-if)#ip bandwidth-percent eigrp 123 100

bandwidth-percentbandwidth-percent Configuration Configuration

NBMA ConfigurationsNBMA ConfigurationsNBMA Configuration Guidelines• EIGRP should not exceed

the CIR of the hub’s serial line (also called the access line).

To do so is called “oversubscribing” the link

• Aggregate traffic of all links to the hub should no exceed the hub’s access line speed.

• Bandwidth on virtual circuits must be the same in both directions.

Hub Router

Point-to-Point NBMAPoint-to-Point NBMAExample of point-to-point Frame Relay with EIGRP• Each spoke router has a

virtual circuit to the hub with a CIR of 256kbps.

• This is an oversubscribed situation.

Why would you want to oversubscribe the spoke routers?

To allow up to 256kbps across each spoke when traffic from other spokes is light.

• Configure the 10 subifs with bandwith of 154kbps so EIGRP will only use 50% of the subif when the NBMA is saturated with user traffic.

256k

256k

256k

256k

256k 256k

256k

256k

256k

256k

Access Line 1.544

Mbps

Point-to-Point ConfigurationsPoint-to-Point ConfigurationsHub_Router(config)#interface serial 0Hub_Router(config-if)#encapsulation frame-relayHub_Router(config-if)#int serial0.1 point-to-pointHub_Router(config-subif)#bandwidth 154Hub_Router(config-subif)#int serial0.2 point-to-pointHub_Router(config-subif)#bandwidth 154. . .Hub_Router(config-subif)#int serial0.10 point-to-pointHub_Router(config-subif)#bandwidth 154

256k

256k

256k

256k 256

k256

k

256k

256k

256k

256k

Access Line

1.544 Mbps

The above configuration insures

EIGRP never uses more than 77kbps for

EIGRP traffic

Each Spoke Router must also be

configured with the same bandwidth as

the Hub Router.

Multipoint EIGRPMultipoint EIGRPIn point-to-multipoint configurations...• If the CIR of each Spoke Router is the same, set

the access line’s bandwidth to the sum of the CIRs

• If the CIR of the Spoke Routers are different, which is the usual case, either...Take the lowest CIR and multiply it by the number of

virtual circuits. This causes higher bandwidth links to be underutilized.

Preferred Hybrid Solution: Use subinterfaces and configure like bandwidth virtual circuits on the same subinterface.

EIGRP & IPX NetworksEIGRP & IPX NetworksEIGRP can optimizes IPX updates.• By default, IPX RIP and EIGRP routes are

redistributed into each process.• If IPX RIP and EIGRP have the same hop count, the

IPX RIP route is believed unless both routes came from the same router.This ensure the router always believes an IPX server over

a Cisco router.

• If EIGRP IPX is running on two neighbor routers, by default on...Serial links, SAP updates are only sent when a change

occursLAN links, SAP updates are sent periodically (60 sec)

– You can configure incremental updates if...» all nodes out the interface are EIGRP peers and» the LAN link is not directly connected to an IPX server

EIGRP IPX ConfigurationsEIGRP IPX ConfigurationsEIGRP and IPX basic routing configurationsRouter(config)#ipx routing

Router(config)#ipx router eigrp AS

To disable IPX RIP updates for a particular network• Since IPX RIP is on by default (no additional

configurations are needed), to disable updates for a specific network...

Router(config)#ipx router rip

Router(config-ipx-router)#no network network-number

To configure incremental SAP updates on LANs...Router(config-if)#ipx sap-incremental eigrp AS [rsup-only]

rsup-only means IPX RIP routing is used. EIGRP is only used for SAP updates. EIGRP routes are ignored.

Monitoring EIGRPMonitoring EIGRP



Monitoring EIGRPMonitoring EIGRPMonitoring Command Description

show ip eigrp neighbors [type number ][details]

displays the neighbor table; can specify interface; details expands the output

show ip eigrp interfaces [type number ][AS ][details]

displays info about each EIGRP interface; options can specify the interface, AS, and expand the output

show ip eigrp topology [AS |[ip-address ][mask ]]

show ip eigrp topology [active|pending|zero-successors]

show ip eigrp topology all-links

show ip eigrp traffic [AS ]displays the number of EIGRP packets sent and received sent the last time the counter was cleared; use to view excessive EIGRP routing updates

debug eigrp fsmObserve the feasible successor activity and determine if routes are being installed and deleted by the EIGRP routing process

debug eigrp packetObserve the transmission and receipt of EIGRP packets including hellos, queries, updates, etc. Sequence numbers are also displayed.

displays the topology table; extra options can fine tune the output; for example: - specify the AS and/or a specific ip address - show only routes in the active state, pending convergence, or routes with no successors - show all routes, not just feasible successors, with the all-links option

Chapter 6 Lab NotesChapter 6 Lab Notes



Lab NotesLab NotesLab 6.7.1: Configuring EIGRP with IGRP• Build a router topology with EIGRP and IGRP routers• Use the show ip route command to note differences in how

external routes are noted: The IGRP route table will denote EIGRP routes with an “I” The EIGRP table will denote IGRP routes with a “D EX”

Lab 6.7.2: Configuring EIGRP Fault Tolerance• Build an EIGRP topology and verify feasible successor• Turn of debug eigrp fsm & observe route flushing

Lab 6.7.3: Configuring EIGRP Summarization• Configure topology with loopbacks• View outputs for auto and manual summarization

Lab 6.8.1: EIGRP Challenge Lab• Four router lab with EIGRP and IGRP Ass• Capture running configs before and after summarization• Verify successful ping to every interface from all routers



AcknowledgementsAcknowledgements

Documents

Table of Contents Basics of EIGRP Basics of EIGRP Configuration EIGRP Configuration Monitoring EIGRP Monitoring EIGRP Chapter 6 Lab Notes Chapter 6 Lab